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_ K NO _ <br /> r f` <br /> A0,011eif G@® YStelm 43255 Mission Blvd. Suite B Fremont,CA 94539 (415)651-1906 <br /> December 16, 1986 <br /> AGS 86102--1 <br /> Mr. Jim McCutchen, <br /> Beacon Oil Company <br /> 525 W. Third Street <br /> Hanford, California 93230 <br /> Subject: Report, subsurface environmental investigation, Beacon <br /> Service Station #3-492, Manteca, California <br /> 'F Dear Mr. McCutchen: <br /> This report presents the results of our limited environmental <br /> investigation at the above-referenced site. Beacon Oil Company <br /> requested that Applied GeoSystems perform this investigation in <br /> response to precision test results on a 10,000 gallon diesel <br /> product tank at the site. It is our understanding that the tank <br /> did not pass a pressure test. The investigation included the <br /> drilling of three boreholes and the construction of three four- <br /> s <br /> inch diameter monitoring wells. <br /> Laboratory analyses of soils from the bo' ringv at the site show <br /> low to moderate concentrations of total hydrocarbons. Water <br /> analyses show low aromatic hydrocarbon (BETX) concentrations. <br /> The benzene levels in,=.•:iter collected from MW-1 and MW-2 are <br /> above Environmental Pr(Ae_—:ion Agency recommended maximum <br /> concentrations for drinking water. It is our understanding, <br /> based on conversations with personnel from the.San.Joaquin Local <br /> Health District, that the shallow aquifers in the vicinity of the <br /> site are used as a drinking water source. Because the shallow <br /> aquifers are used for drinking water, and because the aromatic <br /> hydrocarbon (BETX) concentrations in the water samples from MW-1 <br /> and MW-2 are above drinking water standards, we recommend that <br /> the water of the three wells be subjectively monitored monthly to <br /> assess possible changes in hydrocarbon concentration. This..: <br /> --- --- ---- - subjective-monitoring-should-be-conducted.-far-a-period-of-six <br /> months to 'evaluate possible contaminant trends We further <br /> reo�smtt:end <br /> that the wells be purged, resampled, and analyses for.. <br /> tota ,.hydrvarbon` and hydrocarbon constituent levels after six <br /> months.- Possible recommendations for water treatment to remove <br /> dissolved constituents. will be made based on the results of <br /> monthly subjective and a six month quantitative analyses. <br />